But Bishop and Westerman want to bring Obama administration officials into the firestorm as well.

“A recent spike in concerns about federal officials traveling on non-commercial aircraft for official business has prompted various congressional and media inquiries,” the Republicans wrote, citing a letter by the committee’s top Democrat, Rep. Raúl Grijalva (Ariz.), seeking an inspector general investigation into Zinke.

But Grijalva's letter “selectively avoids the Interior Department spokeswoman’s comments stating that ‘charter or military plane trips were booked only after officials were unable to find commercial flights that would accommodate [your] schedule and that all were ‘pre-cleared by career officials in the ethics office,’’” Bishop and Westerman wrote.

Zinke has dismissed the controversy around his travel as “a little BS” and defended his flights as necessary, appropriate and in line with the law.

The scrutiny over his travel has focused largely on a charter flight costing more than $12,000 to take him from a Las Vegas dinner hosted by a former campaign donor to his home state of Montana.

Since the dinner was so late, he could not take a commercial flight and make it to Montana in time for a meeting the next morning.

He also took a charter plane multiple times in the U.S. Virgin Islands in March.

All the flights were cleared by relevant ethics and legal officials at the Interior Department, the administration has said.